Monitored melt spinning method and apparatus



Oct. 28,1939 I J, R. NICHOLSON MONITORED MELT SPINNING METHOD ANDAPPARATUS Filed Sept. 23. 1965 FIG. 2.

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I NVEN TOR. JAMES R. NICHOLSON j/fl i.

ATTORNEY United States Patent 3,475,523 MONITORED MELT SPINNING METHODAND APPARATUS James R. Nicholson, Pensacola, Fla., assignor to MonsantoCompany, St. Louis, Mo., a corporation of Delaware Filed Sept. 23, 1965,Ser. No. 489,668 Int. Cl. G01d /08, 1/06; F04!) 13/00 US. Cl. 26440 5Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method andapparatus for melt spinning of polymers, wherein the power consumed bythe pump motors is used to determine the condition of the spinningsystem.

In melt spinning of synthetic fibers it is customary to pump a meteredstream of fiber forming viscous polymer through a spinning pack justprior to extrusion through a spinneret. Various abnormal conditions canoccur in such a system, such as plugging of the filter media in aspinning pack, development of channels through the filter media, packleaks, variation in supply of the molten polymer, etc. Early detectionof these defective conditions permits substantially more efficient andeconomical operation of the spinning unit. One prior art approach todetermining such abnormal operation is to mount a mechanical torquegauge on the pump drive shaft. However it is very difficult to keepmechanical gauges properly calibrated, and, since the gauge rotates withthe pump shaft, it is difiicult to read and could pose a safety hazard.It has now been discovered that abnormal operation can be more simplyand reliably determined by monitoring the power consumed by the pump ofa melt spinning apparatus.

Accordingly the primary object of the invention is to provide a methodand apparatus for reliably and accurately detecting certain abnormalspinning conditions. A further object is to provide a method andapparatus of the above character wherein the detection is accomplishedby monitoring the power consumed by the pump motors. Other objects ofthe invention will in part by obvious and will in part appearhereinafter.

For a more complete understanding of the nature and objects of theinvention, reference should be had to the following detailed descriptiontaken in connection with the accompanying drawings, in which:

FIGURE 1 is a schematic vertical sectional view of an exemplary meltspinning apparatus according to the present invention, and

FIGURES 2 and 3 are graphs of pack pressure versus meter pump motorpower requirement, and pack pressure versus spun denier, respectively,for a particular spinning apparatus.

FIGURE 1 illustrates a generalized melt spinning apparatus whereinpolymer flake is introduced into an aperture in the top of a heatedblock assembly 22. The flake is melted by heated fins 24 and falls asmolten polymer into melt pool 26 beneath fins 24. Booster pump 28' isdriven by alternating current motor 30, which may be of induction type,and is submerged in melt pool 26 and supplies molten polymer todistribution passage 32. Close- .tolerance meter pump 34, driven bysynchronous motor 36, has its inlet passage connected to receive thepolymer in passage 32, and pumps a metered output stream into 3,475,523Patented Oct. 28, 1969 chamber 38 for extrusion through spinneret 40. Itshould be understood that in actual practice several metering pumpswould normally be supplied from distribution passage 32. The moltenpolymer extruded through spinneret 40 is illustrated as forming aplurality of filaments 42 which are solidified or cooled by conventionalmeans (not illustrated) and gathered into yarn 44.

A filter or spinning pack 46 is mounted in chamber 38 above spinneret 40to remove gel particles and the like from the molten polymer. Filter 46also imparts desirable shear to the polymer just prior to extrusion, asis well known in the art. Filter 46 may be composed of layers of variousgrades of sand, stacked screens, sintered porous structures, or thelike.

Synchronous motor 36 may be any of the conventional synchronous motorconstructions. Thus it may have a permanent-magnet rotor, a D.C.-excitedrotor, or the motor may be of reluctance synchronous design. Whateverthe type synchronous motor selected, means 48 (illustrated as awattmeter) are provided for detecting the power consumed by motor 36.

FIGURE 2 illustrates the power consumed by such a synchronous motor as afunction of the pressure developed in chamber 38, for an exemplaryembodiment of the invention. As illustrated, motor 36 consumed about 15watts with filter 46 and spinneret 40 removed, and there is asubstantially linear relationship between power consumed and thepressure in chamber 38 (pack pressure), so long as the pressure inpassage 32 is reasonably constant. In normal operation, the pressure inpassage 32 will be reasonably constant.

FIGURE 3 illustrates the relationship between spun denier and packpressure, for an exemplary yarn count. The horizontal dotted linesindicate acceptable denier quality control limits. Therefore, for thisparticular yarn count the minimum spinning pressure is around 1700p.s.i. (pounds per square inch) and the maximum spinning pressure isnear 5800 p.s.i., corresponding to meter pump wattages of about 30 andrespectively.

During normal operation of the FIGURE 1 system, as filter 46 traps andremoves gel or other impurities, the resistance presented by filter 46slowly increases and therefore the pressure in chamber 38 goes up. Thiscontinues until the denier of the spun yarn decreases below acceptablequality control levels because of increased slippage in pump 34, oruntil a leak develops. If the filter is replaced before the pressurebuilds up to this critical level, a considerable reduction in productionof off-grade or defective low denier yarn is achieved since the spinningunit may spin olT-grade yarn for many hours before the defectivecondition is detected by actual measurement of the yarn denier. If relaycontacts are added to meter 48' to form a meter relay, a simple alarm orlight 49 may be activated whenever the meter pump wattage varies outsidethe predetermined limits of normal operation, thus detecting defectiveyarn as soon as it is spun without the necessity of visual monitoring ofthe meter.

In the usual construction booster pump 28 supplies more polymer todistribution passage 32 than is pumped by metering pump 34. In such aconstruction, booster pump 28 has a relief orifice on its output side,to discharge the excess polymer back to melt pool 26. On occasion thisrelief orifice becomes plugged and causes a sharp increase in pressurein passage 32. This reduces the pressure difference across meter pump 34and causes an increase in spun denier. Conversely, if booster pump 32suffers a loss of polymer supply due to a temporary lowering of the meltrate, the pressure in distribution passage 32 drops or becomes variable.This condition will result in production of low or variable denier yarn.Either of these conditions (plugging of the relief orifice or loss ofpolymer supply) causes substantial variations in the power consumed bybooster motor 30. Similar to meter 48, relay contacts may be added tometer 50, in order to actuate a light or alarm 52 when the powerconsumed by motor 30 varies outside a pre-determined range. Alarms 49and 52 can be combined, if desired.

A comparison of the readings of wattmeters 48 and 50 can usuallyidentify the type of abnormal condition. Thus if meter 50 maintains itsnormal reading while meter 48 indicates an abnormally high reading, thedefective condition is an abnormal increase in the resistance of filter46. If, on the other hand meter 50 reads an abnormally low wattage whilemeter 48 indicates a normal or low wattage, the failure is a loss ofpolymer supply to the booster pump 28. Othere defective conditions aresimilarly indicated by other comparisons of meter readings.

It should be understood that the power measuring means 48 and 50 neednot necessarily include a conventional meter as such, but could includeother means responsive to the levels of power consumed by motors 30 and36. Monitoring the power of the meter pump motor according to theinvention is not restricted to metering pump supplied from meltedpolymer flake, but may be applied to metering pumps fed directly from apolymerizer. In any case where a plurality of spinning positions are tobe monitored, it may be desirable to provide a scanning mechanismwhereby a single power-measuring means is connected, as by a steppingswitch, to sequentially measure the power consumed in several motors.Provision of a suitable scanning mechanism is well within the scope ofone skilled in the art.

The invention has proved to be of substantial economic significance. Inone particular extended comparison with control spinning, application ofthe invention permitted the reduction of low denier yarn by 62%,reduction of pack leaks by 56%, and provided a significant improvementin overall denier uniformity.

It may be seen that the invention as above disclosed provides asubstantial improvement in the art of spinning of artificial fibers. Theapparatus necessary for practice of the invention is simple andreliable, and provides economic advantages greatly in excess of the costof the additional apparatus. If separate power measuring means areprovided for the meter pump motor 36 and the booster pump motor 30, thecause of failure of the unit can be determined with considerableassurance before the equipment is disassembled for repair. In addition,the power measuring system herein disclosed permits each unit to beoperated until the pack pressure actually increases to an unsatisfactorylevel, rather than disassembling all units after some arbitrary time inservice has elapsed.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efiiciently attained and,since certain changes may be made in carrying out the above method andin the construction set forth without departing from the scope of theinvention, it is intended that all matter contained in the abovedescription or shown in the accompanying drawing shall be interpreted asillustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secureby Letters Patent is:

1. In a spinning process wherein a meter pump supplies polymer through afilter media, and wherein said pump is driven by a synchronous motor,the improvement comprising in combination:

(a) selecting said filter media so that said motor initially consumespower within a pre-determined range of wattage,

(b) and detecting when said power varies outside said pre-determinedrange of wattage.

2. In apparatus for melt spinning filaments from a molten polymer,wherein a synchronous motor drives a meter pump for supplying moltenpolymer through a spinning pack to a spinneret for extrusion to formfilaments, the combination therewith of (a) means for measuring thepower consumed by said motor,

(b) and means, responsive to variations of said power outside apre-determined range of variations, for detecting abnormal operation ofsaid apparatus.

3. In apparatus for melt spinning filaments from a molten polymer,wherein an alternating current drives a booster pump for supplyingmolten polymer to a meter pump, the combination therewith of:

(a) means for measuring the power consumed by said motor,

(b) and means, responsive to variations of said power outside apre-determined range of variations, for detecting abnormal operation ofsaid apparatus.

4. The process defined in claim 1, further comprising:

(a) supplying polymer through a distribution passageway to the inlet ofsaid meter pump from a booster pump driven by a further motor; and

(b) detecting when the power consumed by said further motor variesoutside a further predetermined range of wattage.

5. The process defined in claim 4, further comprising normallyre-circulating a portion of the output of said booster pump to thepolymer input supply for said booster pump.

References Cited UNITED STATES PATENTS 2,540,146 2/1951 Stober 264402,566,854 9/1951 Rhodes 264-40 3,002,226 10/1961 Warthen 26440 3,347,96010/1967 Fenley 264-210 3,391,232 7/1968 Jackson 26440 DONALD J. ARNOLD,Primary Examiner US. Cl. X.R. l88; 264-176

